It is known that liquid petroleum gas (LPG) can be produced by converting naphtha or like materials by cracking, such as hydrocracking. Known processes to convert naphtha like material to LPG all suffer from either producing an LPG quality that has an undesirably high ratio of C4 hydrocarbons (hereinafter C# hydrocarbons are sometimes referred as C#, wherein # is a positive integer) to C3 hydrocarbons or an excessive production of methane. The undesirably high ratio of C4 hydrocarbons to C3 hydrocarbons results in an unbalance in the volumes of C3 and C4 derivatives/products obtained compared to petrochemical demand. The excessive production of methane is caused when the severity of the hydrocracking is increased to shift the products slate to ethane and propane as desired products.
In the prior art, such as in published patent applications WO2012/071137 and GB1148967, focus has been on maximizing C2. This results in high methane production as well. Alternatively, published U.S. Pat. No. 6,379,533, U.S. Pat. No. 3,718,575, U.S. Pat. No. 3,579,434 and others focus on LPG production including C4. This LPG does not constitute a desired feed for steam cracking for producing particularly useful products such as ethylene and propylene.
For application of LPG as fuel, the C3/C4 ratio is not very relevant, explaining the limited amount of development in this area. WO2012/071137 and GB1148967 describe recycling of C4+ material to maximize ethane production. To limit the size of the recycle stream, this implies a rather high severity in the (single) hydrocracking reactor provided, resulting in excessive methane production. Furthermore, WO2012/071137 and GB1148967 describe no equivalent of a hydrocracking process which results in benzene, toluene, xylene (BTX) product.
Among others, U.S. Pat. No. 6,379,533 and U.S. Pat. No. 3,718,575 describe a (integrated) multi-stage hydrocracking approach but solely aim at producing LPG with no control over the C3 to C4 ratio or the total amount of C4's being produced. As indicated above, this is a problem when not producing LPG fuels but petrochemicals derived from the C3 and C4 contained in the LPG.
With the demand for C4 derivatives possibly being smaller than for C3 derivatives, it would be desirable to control the amount of C4 produced. It is further desirable to control the composition of the C4 product (normal versus iso-butanes) as this will determine the ratio between the different C4 derivatives that will be produced.
There is a need in the industry for a process for producing C2 and C3 hydrocarbons with a relatively high yield.